(Reuters) - Iran's supreme leader and the shadowy Quds Force covert operations unit were likely aware of an alleged plot to kill Saudi Arabia's ambassador to the United States, but hard evidence of that is scant, U.S. officials said on Wednesday.

The United States does not have solid information about "exactly how high it goes," one official said.
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Arbabsiar's wife, Martha Guerrero, told KVUE TV station in Austin, Texas, he was innocent. "I may not be living with him, being separated, but I cannot for the life of me think that he would be capable of doing that," she was quoted as saying.
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"We would expect to see the Quds Force cover their tracks more effectively," said one official. Another said a plot to launch a violent attack inside the United States was "very outside the pattern" of recent Quds Force activities.

Kenneth Katzman, an Iran specialist at the Congressional Research Service, said there were elements of the alleged plot that did not make sense.

"The idea of using a Texas car salesman who is not really a Quds Force person himself, who has been in residence in the United States many years, that doesn't add up," Katzman said.

"There could have been some contact on this with the Quds Force, but the idea that this was some sort of directed, vetted, fully thought-through plot, approved at high levels in Tehran leadership I think defies credulity," he said.